1. Field of the Invention
The present description relates generally to switching voltage regulators.
2. Description of the Related Art
Switched-mode voltage regulators provide superior voltage conversion efficiency because they regulate an output voltage with transistor switches that are either on or off so that they never operate in the linear region in which both current and voltage are nonzero. Because at least one of transistor current and voltage is therefore always close to zero, dissipation is greatly reduced so that the regulator efficiency is quite high.
These regulators often operate in two different operational modes. When current demand is medium to high, they preferably operate in a pulse-width modulation mode in which transistor currents are switched on and off during each clock period. When current demand is low, they preferably operate in a pulse-frequency modulation operational mode in which transistor currents are briefly switched on when an output voltage drops below a predetermined threshold. The latter mode enhances operational efficiency during low current demand because it reduces switching losses in the transistor switches. In the pulse-width modulation mode, the switching duty cycle corresponds to the current drain whereas in pulse-frequency modulation mode, the switching frequency corresponds to the current drain.